Laboratory analysis of biological fluids such as blood, spinal fluid, cell cultures and urine can include microscopic examination of a specimen liquid to determine the presence or concentration of suspended particulate matter such as cells. Typically, microscopic examination of liquid specimens has been accomplished by placing a drop of the specimen liquid on a flat transparent microscope slide and then placing a thin flat transparent coverslip over the specimen. The weight of the coverslip and the inherent capillation between the liquid specimen the microscope slide and the coverslip retains the coverslip on the slide and distributes the liquid as a film in the space between the slide and the coverslip. The slide is then placed on a microscope stage and the liquid specimen between the slide and the coverslip is examined.
The procedures involved in preparing slide, liquid specimen and coverslip combinations for optical examination requires an excessive amount of manual manipulation which inevitably results in uncontrollable and unpredictable variations in the specimen examined. An inevitable and most critical variation resulting from use of the above described slide/coverslip combination is the thickness of the specimen between the slide and the coverslip. This variation is important because when a microscopic examination of the specimen is made such examination is over an area of the specimen and provides a count of selected particulate species. Determination of the useful parameter--concentration of particulate species--requires the multiplication of the examined area by the depth of the specimen to obtain the volume of specimen in which the counted particulate matter is suspended. To determine relative concentration differences between counted particulate species in multiple specimens or to determine concentration differences between a selected specimen and a standard specimen the thickness of each specimen must be essentially equal or again must be known so that calculations of volumes in which the particulate species are suspended can be made. Assumptions regarding the thickness of liquid specimens are not useful because uncontrollable variables such as variations in the surface tension from sample to sample which substantially effects thickness, variations in the amount of liquid used for preparing slide specimens, entrapment of air between the slide and coverslip and variations in the pressure exerted between the coverslip and the slide all cause differences in specimen thickness. Further, degrading the utility of such microscopic counts are perturbations in the distribution of particulates in specimens caused by inadvertent translational movement of coverslips with respect to slides during preparation of slide/coverslip assemblies which can result in non-uniformity of the distribution of particulates in specimens.
Attempts have been made to provide inspection slides which avoid the above described limitations of separate slide/coverslip combinations. Some of these efforts have been based on molding unitary transparent plastic slide/coverslip structures with a liquid specimen drawn into examination chambers by capillation. Such devices are disclosed in U.S. Pat. Nos. 3,961,346; 3,777,283; and 4,299,441. Other efforts include fabrication of examination chambers from two plastic molded components bonded or attached together as slide/coverslip structures into which again liquid specimens are drawn by capillation. Such devices are disclosed in U.S. Pat. No. 3,565,537 and United Kingdom Application No. 2,127,557A. All of these attempts to provide useful inspection slide designs have failed due to such deficiencies as: inability to bleed off entraped gases in the examination chambers; failure to provide parallel floor and roof surfaces for the examination chambers which are accurately distanced from each other; failure to provide sample chambers which have thicknesses less than the depth of field of optical instruments used to examine specimens which can cause eye fatigue to the technician who is required to refocus the instrument in order to complete an examination of a specimen; failure to provide bonding systems for accurate positioning of slide/coverslip structures such as that disclosed in U.S. Pat. No. 3,565,537 which includes no expansion space for melted bonding ridges thereby precluding accurate positioning; or including excessively large openings from the examination chambers which enhance evaporation of specimen fluids and accordingly decrease the time between charging an examination chamber and the time when the specimen must be examined.